1. Field of the Invention
The present invention relates to a gear-shifting transmission apparatus for a bicycle, and to a bicycle incorporating the apparatus. More particularly, the invention relates to a transmission mechanism of the type using a one-way clutch and slide mechanism.
2. Background Art
In a bicycle disclosed in Japanese Patent Publication No. 2004-155280, a transmission is provided in which a transmission position can be switched to multiple speeds by a derailleur. In the transmission, a drive sprocket coupled in a driven manner to a crankshaft with a one-way clutch interposed therebetween moves in an axial direction in response to a movement of a chain in the axial direction when the chain is shifted between plural transmission sprockets. Therefore, in a torque transmission path between the one-way clutch and the drive sprocket, a slide mechanism is provided, which, when the crankshaft rotates positively, transmits torque of the crankshaft through the one-way clutch to the drive sprocket, thereby rotating the drive sprocket integrally with the crankshaft, and making the drive sprocket movable with respect to the crankshaft in the axial direction. The slide mechanism is composed of a ball spline mechanism including plural balls arranged between an inner cylinder and an outer cylinder and housed in housing grooves formed on the inner cylinder and the outer cylinder. Moreover, in the inner cylinder formed of one member, molded integrally therewith are a stopper for regulating a movement of the balls in the axial direction in the housing grooves, thereby regulating movement ranges of the drive sprocket and the outer cylinder in the axial direction, and a clutch outer body of the one-way clutch. Furthermore, the stopper is located between the housing grooves and the clutch outer body to the axial direction.
In the conventional technology described above, the stopper and the clutch outer body are integrally molded in the inner cylinder of the ball spline mechanism. Accordingly, the housing grooves are formed into a dead-end shape formed in a range from one end of the inner cylinder to a halfway thereof in the axial direction, and the housing grooves cannot be formed by means of machining capable of performing a grooving process at low cost, for example, broaching. Therefore, cost caused by the machining is increased, and eventually, cost of the transmission is increased. Moreover, the stopper is subjected to the integral molding, and a restriction thus also occurs in machining for an inner peripheral surface of the clutch outer body, with which clutch elements are to be engaged, thus also resulting in an increase of the processing cost.